linux-kernel - [PATCH 31/29] x86/boot/e820: Move index increments outside accessors in e820__update

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Message-ID: <aCXQ2mdVU_D4tFiS@gmail.com>
Date: Thu, 15 May 2025 13:32:42 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Andy Shevchenko <andy@...nel.org>
Cc: linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
	Borislav Petkov <bp@...en8.de>, Juergen Gross <jgross@...e.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Rapoport <rppt@...nel.org>,
	Paul Menzel <pmenzel@...gen.mpg.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Woodhouse <dwmw@...zon.co.uk>
Subject: [PATCH 31/29] x86/boot/e820: Move index increments outside accessors
 in e820__update_table()


* Andy Shevchenko <andy@...nel.org> wrote:

> On Mon, Apr 21, 2025 at 08:51:57PM +0200, Ingo Molnar wrote:
> 
> ...
> 
> > +	int idx;
> 
> > +	u32 idx, chg_idx, chg_nr;
> 
> What about sanitizing the type as well to be let's say unsigned int idx in all cases?

Not sure - I kind of like the brevity of 'u32' here, and it's also the 
type of the originating ABI interface.


> ...
> 
> > +			change_point[chg_idx]->addr	= entries[idx].addr;
> > +			change_point[chg_idx++]->entry	= &entries[idx];
> > +			change_point[chg_idx]->addr	= entries[idx].addr + entries[idx].size;
> > +			change_point[chg_idx++]->entry	= &entries[idx];
> 
> Does GCC 15 not produce any warnings here? Linus recently complain on some code
> with index increment inside the accessor. Perhaps just
> 
> 			change_point[chg_idx]->entry	= &entries[idx];
> 			chg_idx++;
> 
> ?

Yeah, good point - patch attached.

Thanks,

	Ingo

===================================>
From: Ingo Molnar <mingo@...nel.org>
Date: Thu, 15 May 2025 13:26:46 +0200
Subject: [PATCH] x86/boot/e820: Move index increments outside accessors in e820__update_table()

This kind of code:

	change_point[chg_idx++]->entry  = &entries[idx];

Can be a bit confusing to human readers, and GCC-15 started
warning about these patterns.

Move the index increment outside the accessor.

Suggested-by: Andy Shevchenko <andy@...nel.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Arnd Bergmann <arnd@...nel.org>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Rapoport (Microsoft) <rppt@...nel.org>
---
 arch/x86/kernel/e820.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index aadc46f3d074..b758c0632d0c 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -421,9 +421,11 @@ __init int e820__update_table(struct e820_table *table)
 	for (idx = 0; idx < table->nr_entries; idx++)	{
 		if (entries[idx].size != 0) {
 			change_point[chg_idx]->addr	= entries[idx].addr;
-			change_point[chg_idx++]->entry	= &entries[idx];
+			change_point[chg_idx]->entry	= &entries[idx];
+			chg_idx++;
 			change_point[chg_idx]->addr	= entries[idx].addr + entries[idx].size;
-			change_point[chg_idx++]->entry	= &entries[idx];
+			change_point[chg_idx]->entry	= &entries[idx];
+			chg_idx++;
 		}
 	}
 	chg_nr = chg_idx;